Glucose and glycogen are known to be substrates for anaerobic metabolism during cardiac anoxia. Previous investigations indicate that the utilization of glucose or glycogen by the anoxic myocardium has a protective effect upon the heart. The objective of this project is to evaluate the protective effect of increasing anaerobic energy substrate available to the anoxic arrested heart by supplying glucose or elevating glycogen stores. Dogs will be used as the experimental animals, and ischemic cardiac arrest will be produced during cardiopulmonary bypass. Cardiac function prior to and following cardiac arrest is to be evaluated in animals with increased cardiac glycogen content and in animals with glucose administration during anoxia as compared to controls. The major emphasis will be on the relationship between carbohydrate utilization during anoxic arrest and subsequent left ventricular function. In selected experiments structural changes will be studied by histologic and electronmicroscopic techniques. The effects of temperature and pH upon utilization of glucose and glycogen during anaerobic metabolism are to be defined, and the relationship between carbohydrate utilization and tissue potassium concetration is to be studied. Efficient methods of increasing myocardial glycogen levels and providing available glucose substrate to the anoxic heart are to be also evaluated.